A Lassa Fever Vaccine Trial in Adults and Children Residing in West Africa

Inclusion Criteria: * Adults, adolescents, and children in good general health as assessed by medical history and physical examination (group-specific criteria apply). * At least 18 months old on the day of screening and not more than 70 years old on the day of vaccination (group-specific criteria apply). * Participant or parent/guardian willing to comply with the requirements of the protocol and available for follow-up for the planned duration of the study. * In the opinion of the Principal Investigator (PI) or designee and based on Assessment of Informed Consent Understanding (AOU), participant or parent/guardian has understood the information provided and potential impact and/or risks linked to administration and participation in the trial; written informed consent will be obtained before any study-related procedures are performed. Children old enough to understand the procedures will be asked to assent, in addition to parent/guardian consent, in accordance with local requirements. * Willing to undergo HIV testing, risk reduction counselling, and receive HIV test results (group-specific timepoints apply). * All participants of child-bearing potential engaging in sexual activity that could lead to pregnancy must commit to use an effective hormonal contraception or intrauterine device beginning 2 weeks prior and extending for 4 months following receipt of vaccine/placebo. Study sites will choose which methods are most appropriate for their population and this will be specif…